I2C/SPI Tap

Note

This page is for the I2C/SPI Tap Tap plugin. For the board, please see the “Hardware Manual”.

The I2C/SPI Tap for IO Ninja is a hardware sniffer for monitoring I2C and SPI communications. Our sniffer allows you to tap into the lines of I2C and SPI links and immediately view the captured data bytes in IO Ninja software — in real time and using our innovative dual-hex view tailor-suited for the inherently full-duplex SPI data. Use this plugin to monitor all communications.

Basic Setup

Ensure your I2C/SPI Tap is connected to your computer.

Please see the “IO Ninja Hardware Manual” for guidance on doing so.

In IO Ninja, click the “New Session” dropdown and select a new “I2C/SPI Tap” session.

If not selected automatically, select your I2C/SPI Tap from the “Tap:” dropdown.

Select either “SPI” or “I2C” from the “Protocol:” dropdown.

Start capturing by clicking the “Capture” button located to the right of the “Protocol:” dropdown.

Monitor communications in the “I2C/SPI Tap” tab.

Adjust settings as needed via the “Settings” button (see “Settings” section below for details).

Settings

Setting	Description	Default
Tap	The I2C/SPI Tap that should be used.
Protocol	The protocol to be used, either `I2C` or `SPI`.	SPI
SPI mode	Determines when data is sampled and shifted based on the clock polarity (`CPOL`) and clock phase (`CPHA`). See available options.	SPI-0 (CPOL 0, CPHA 0)
SPI data bits	Number of bits sent in each transaction from master to slave (or vice versa). See available options.	8 bits
SPI endianness	The order in which individual bits within a byte or word are transmitted on the data line. See available options.	Big-endian (MSBit first)
Flip SPI MOSI/MISO	Flip the `MOSI`/`MISO` roles without rewiring.	False
Use update rate limit	Only allow a specified number of log scroll operations per second.	True
Update rate limit	The number of log scroll operations allowed per second.	16
Read parallelism (Windows-only)	Maximum number of read requests to issue in parallel. Having more than one pending read at a time helps with increasing read throughput when incoming data arrives in rapid streams (after filling one user buffer, the kernel can immediately switch to the next one without any waiting). Increasing this number beyond 4 usually won’t yield any extra performance gains.	4
Read block size (B)	The size of each individual read block submitted to the underlying transport.	4KB
RX buffer size (B)	The full size of the incoming data (RX) buffer. Affects read throughput.	16KB
Keep read block size	Don’t merge read blocks in RX buffer. Incoming data blocks coming in quick succession can be merged together so that IO Ninja writes them to log as a whole. When this option is set to `True`, blocks are written to the log without merging, i.e., exactly as they are received from the underlying transport..	False
RX buffer full notifications	Toggle warnings in log about the incoming data (RX) buffer getting full.	False

SPI Mode Options

Option	Description
SPI-0 (CPOL 0, CPHA 0)	Clock starts low, data is read on rising edge.
SPI-1 (CPOL 0, CPHA 1)	Clock starts low, data is read on falling edge.
SPI-2 (CPOL 1, CPHA 0)	Clock starts high, data is read on falling edge.
SPI-3 (CPOL 1, CPHA 1)	Clock starts high, data is read on rising edge.

SPI Data Bit Options

Option
4 bits
8 bits
12 bits
16 bits

SPI Endianness Options

Option	Description
Little-endian (LSBit first)	The least significant bit is transmitted first, meaning data is shifted out starting with the rightmost bit. This is less common and typically used only when a specific device requires it.
Big-endian (MSBit first)	The most significant bit is transmitted first, starting with the leftmost bit of the byte or word. This is the standard and most widely used format in SPI communications.